We present a mid-infrared spectroscopic data cube of the central part of
30 Doradus, observed with Spitzer's Infrared Spectrograph and Multiband
Imaging Photometer for Spitzer/spectral energy distribution mode.
Aromatic dust emission features and emission lines from molecular and
atomic hydrogen are detected but they are not particularly strong. The
dominant spectral features are emission lines from moderately ionized
species of argon, neon, and sulfur, which are used to determine the
physical conditions in the ionized gas. The ionized gas excitation shows
strong variations on parsec scales, some of which can plausibly be
associated with individual hot stars. We fit the ionic line strengths
with photoionization and shock models, and find that photoionization
dominates in the region. The ionization parameter U traces the rim of
the central bubble, as well as highlighting isolated sources of
ionization, and at least one quiescent clump. The hardness of the
ionizing radiation field T rad reveals several "hot spots"
that are either the result of individual very hot stars or trace the
propagation of the diffuse ionizing field through the surrounding
neutral cloud. Consistent with other measurements of giant H II regions,
log(U) ranges between -3 and -0.75, and T rad between 30,000
and 85,000 K.